This invention relates to continuous rotary drum filters. In these filters, the filter drum operates in a vat receiving a supply of feed pulp or a feed suspension to be subjected to filtration in a manner well known in the art.
The invention by way of example is herein illustrated as embodied in the rotary vacuum drym type filter unit, and will herein be referred to and described accordingly. The end trunnions of the drum are supported in bearings associated with the end walls of the vat in fixed relationship therewith.
More in particular, this invention relates to improvements in the agitator mechanism employed in these filter units for the purpose of preventing sedimentation and accumulation of pulp solids on the bottom of the vat, the bottom usually having a curvature substantially conforming to the peripheral curvature of the filter drum. Small oscillating movements are imparted to the agitator about an horizontal axis parallel to the drum axis, so as to keep the pulp solids in suspension in the vat.
A conventional agitator mechanism comprises an agitator frame structure interposed between the bottom portion of the drum and the bottom of the vat. This agitator frame structure is shaped so as to conform substantially to the curvature of the drum, extending from end to end of the drum.
The ends of the agitator frame structure are supported for said oscillating movement about an horizontal axis extending parallel to the drum axis, and spaced vertically below the drum axis a distance such that the support bearing means for the agitator frame structure can be accommodated below the trunnions of the filter drum. Drive means operatively connected or linked to both ends of the agitator frame structure, are provided for imparting those small oscillating movements symmetrically to said frame structure.
In a preferred embodiment, illustrating the invention, the suspension of the agitator structure is implemented by a pair of frictionless so-called "torsion bearings" defining the horizontal axis of oscillation, and containing a rubber filler which absorbs the oscillation by internal torsional deformation of the rubber, and also cushions the reversal of movement of the oscillations. However, this does not exclude the use of other types of bearings in connection with this invention, for example sleeve bearings which may have a self lubricating bearing liner or the like. These alternatives are herein covered by the generic term "oscillatory bearing".
In the torsion bearing a rubber filter in the form of a thick walled rubber sleeve or thick walled annular rubber member tightly surrounds a center pin, secured thereto as by bonding, against rotational slippage of the rubber relative to the pin. The rubber bearing sleeve in turn is surrounded and tightly confined by a housing which comprises a bearing base portion and a bearing cap, both parts being bolted together in a manner whereby the rubber sleeve or filler is compressed sufficient to preclude rotational slippage between the rubber and the housing. The wall thickness radially of the rubber sleeve is such that a torque force applied to the housing by the oscillations, will be absorbed by torsional deformation or torsional "give" of the rubber, relative to the fixed center pin.
In the present context of the earlier construction of the agitator mechanism, the base portion or underside of the torsion bearing heretofore has been rigidly bolted to respective end suspension members or end plates extending rigidly from the agitator frame structure. Consequently, when the oscillating movement is imparted to the thus suspended agitator frame, that movement, through the housing of the torsion bearing, is absorbed by a corresponding degree of internal torsional of angular deformation of the rubber sleeve material, alternatingly in both directions.
When undue wear of the rubber sleeve material heretofore manifested itself, the bolts of the rigid suspension connection had to be removed to detach the agitator frame structure, when replacement of the torsion bearing was required.
A problem heretofore encountered in the operation and maintenance of the earlier agitator mechanism, was found in the appearance of premature wear and tear of the torsion rubber sleeve, manifesting itself in bumpy operation of the mechanism.
The problem, according to this invention, is attributable to non-torsional uneven transverse bearing stresses exerted upon the rubber sleeve, tending to squeeze the rubber material laterally out from the confinement in the bearing housing, and necessitating shutdown of the machine, and replacement of the torsion bearing or else of the center pin with rubber sleeve.
It was visualized that such deterioration of the rubber filler would develop, for instance, when uneven concentrated transverse bearing pressure is exerted upon the one or the other end of the rubber sleeve, as may be caused due to inaccuracies in alignment or construction of the agitator mechanism, or due to elastic deformation of the agitator frame, especially when considering the great length of the agitator structure, which may be between 20 feet and 30 feet.
Replacement of the torsion bearing would require shutdown of the machine, temporarily supporting the weight of the agitator structure so as to allow for disconnecting the agitator structure, and detaching the ends of the non-turnable bearing pin from its fixed supports. This releases the torsion bearing for replacement.
In view of the above stated problem, it is an object of this invention, to provide an improved agitator mechanism embodying means whereby the causes of the aforementioned undesirable stress effects upon the rubber filter of the torsion bearing are compensated for, and the number of shutdowns and bearing replacements are minimized or rendered largely avoidable.